Light source devices for use in image reading devices and the like are used in facsimile machines, multifunctional devices, or devices for reading valuable papers and the like. Such an image reading device irradiates a document or paper to be read with light from a light source device in multiple directions. Light reflected by or transmitted through such an object to be read is imaged by the image reading device through an imaging element such as a lens and a mirror onto a photoelectric conversion element such as a complementary metal-oxide semiconductor (CMOS) sensor and a charge-coupled device (CCD) sensor to detect optical information of the object to be read. The image reading device utilizes the obtained image information for copying of documents, authenticity check of paper currency, check of level of degradation due to distribution, or the like. The reduced size of image reading devices and increased reading speed in recent years require that the light source devices become miniaturized and highly efficient.
Some conventional light source devices requiring such irradiation in multiple directions are as follows. For example, Patent Literature 1 describes an image reading device that irradiates an object to be read with light in multiple directions using a single light guide and a mirror.
Patent Literature 2 discloses a bifurcated light guide obtained from a single light guide by disposing light diverting surfaces in multiple positions of the single light guide in such a way that the vertical planes extending in the longitudinal direction of the light diverting surfaces intersect (see FIG. 2). Patent Literature 2 also discloses a light guide having one light diverting surface and two exit portions (portions having faces from which light exits) (see FIG. 10).
Patent Literature 3 discloses a light source device used for document reading, the light source device including a linear light source, a rod-shaped lens arranged in parallel to the linear light source, and a linear reflector arranged, at the opposite side of the rod-shaped lens from the linear light source, in parallel to the rod-shaped lens at a position to intersect a second optical axis plane of the rod-shaped lens. The rod-shaped lens has a first optical axis plane containing optical axes passing through a first linear focal point group containing first focal points and a second optical axis plane containing optical axes passing through a second linear focal point group containing second focal points. The first linear focal point group and the second linear focal point group are located in the vicinity of the position where the second optical axis plane of light reflected by the linear reflector intersects the first optical axis plane.